Data storage media have been introduced onto which data may be written only once but read many times. Such media is referred to as Write-Once, Read Many, or WORM for short. The advantages of such media are many fold, and include the ability to enhance enforcement of copyrights.
In part because legal rights are involved with WORM media, government regulations have arisen that are related to WORM media. Non-compliance with applicable regulations may incur severe penalty under some of the rules. Notable among current regulations is SEC rule 17a-4, which not only requires data to be reliably stored on “non-erasable” and “non-rewritable” media, but also requires enforcement of data retention policy and data shredding, which, as set forth below, are competing requirements owing to the nature of WORM media.
In greater detail, three types of WORM media exist. The first is so-called physical WORM, or “P-WORM”, in which WORM requirements are imposed by the physical characteristics of the media. Among P-WORM media are optical disks. Electronic WORM, or “E-WORM”, such as WORM tapes are a second form of WORM, in which WORM requirements are imposed by the electrical characteristics of the media. Yet a third type of WORM is software WORM, or “S-WORM”, in which WORM requirements axe imposed through software interlocks.
As critically recognized herein, existing P-WORM and E-WORM systems which, recall, use optical media and magnetic tapes, respectively, are having trouble keeping pace with current performance and capacity requirements for storing regulated data. The S-WORM systems attempt to solve this problem by storing data on rewritable magnetic disks, which have good performance in terms of speed and capacity, and relying on software for WORM safeguards. The disadvantage of S-WORM, however, is that it offers a weaker WORM guarantee than P-WORM or E-WORM.
As further understood by the present invention, regardless of the type of WORM, requirements exist for securely disposing (“shredding”) of data on WORM media, e.g., regulations might dictate that sensitive data be completely erased at the end of the documentation retention period. With the relatively weaker S-WORM, shredding can be done relatively easily, by overwriting the data multiple times using selected bit patterns, and sometimes under different temperatures to eliminate off-track remnants of old data. In contrast, with stronger P-WORM and E-WORM systems, data shredding currently must be undertaken by physical destroying the media or by using special hardware to overwrite the data. The present invention understands that such shredding is cumbersome and expensive: not only does it require human intervention (and, when the media is not to be completely destroyed, costly hardware), it is also inefficient because such shredding typically occurs at a much coarser granularity compared with the minimum unit size for writing into the WORM media.